Electric-fttrnace regulator



Mar. 20, 1923.

J. A. SEEDE suacwmc FURNACE nmuuwon Filed Feb.

Inventcr: Jo'hn A. seeds,

Hie Attorney.

Patented Mar. 20, 1923.

UNITED STATES PATENT OFFICE.

JOHN A. SEEDE, OF SC'HE'NECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC- FU RNACE REGULATOR.

Application filed February 4, 1920. Serial No. 356,193.

T all whom it may concern:

Be it known that I, JOHN A. Scene. a cit izen of the United States, residing at Schenectad county of Schenectady, State of New ork, have invented certain new and useful Improvements in Electric-Furnace Regulators, of which the following is a specification.

The present invention relates to electric furnace control apparatus, and it is the object of the invention to prevent disturbances to electric furnace operations, particularly in arc furnaces.

Arc furnaces commonly contain at least one movable electrode the arcing relation of which to another electrode is regulated by suitable control apparatus responsive to the current in the furnace circuit. When the arcin the furnace becomes undulylengthened the operating current decreases as a consequence and this decrease sets into motion the control apparatus to shorten the arc.

Itsometimes happensthat the current is decreased due to some cause external to the andin that case the regulating apparatus may cause the electrode to come into contact with the charge. Other causes may prevent. the-regulating apparatus from main-. tai'ning a suitable length of are. Contact between a; carbon electrode and the charge ma have a very deleterious effect, particular ...when the charge consists of a bath of stee .which ireadily. combines with carbon.

.In accordance with my present invention 'contact between the movable electrode and the charge constituting the co-operating are electrode isprevented by providin the regulating apparatus with means ren ering the same inoperative when the arc voltage falls below a predetermined value.

The accompanying drawing illustrates diagrammatically one embodiment of my in vention applied to a single arc furnace.

Referring to the drawing, an arc furnace is diagrammatically-indicated by dotted rectangle 1. The co-operating electrodes 2, 3, are connected by supply conductors 4, to the secondary windings 6 of a transformer, the primary 7 of which is connected by conductors 8 to a source of alternating current, not shown in the drawing. The electrode 2 is shown as a movable electrode and usually consists of Carbon or graphite, and com monly the stationary electrode 3 at the base of the furnace is constituted by the charge in the furnace, such, for example, as a bath of iron or steel. The electrode 2 is fed toward the bath at a suitable rate to compen sate for electrode consumption.

An electric motor 9 is mechanically connected to the electrode 2 by any form of suitable gearing, the drawing showing a speed reducing gear 10 driven by the motor acting on a nut 11 on the screw-threaded rod 12 to raise and lower the electrode. The electric motor 9 is controlled by suitable switches hereinafter described, to raise or lower the electrodes in response to variations of current in the supply circuit. For this purpose a contact ma 'ng magnet 13 is connected to the secondary 14 of a current transformer, the primary of which is constituted by a portion of the supply conductor 4. The armature of this magnet is connected to a switch lever 14 operating to make contact with either conductors 15 or 16 leading, to suitable contactors. hAnfadjustable resistance 17 is connected across the winding of.

the magnet 13 in order to enable thesetting of the magnet to be varied at will. In circuit with conductor, 15 is a. contactor 18. connected to the armature of '9. volt' controlled megnet l9 which isconneote l adjacent the furnace across the conductors 4and 5 and in shunt to thearcbetween the electrodesQ ands. j

The cycle of operation is as follows, assuming electrodes 2 and 3 to be in contact when a runis started.-

When the tran s former is energized, the magnet 19 pulls up its 'armature'and bridges the contacts 20 in the circuit 15, and the magnet 13 also pulls up its armature and completes a circuit from the conductors 24, 16 and to energize thecontactor magnet 26, and cause it=tc pull up its armature, thereby closing the contacts 27 and 28. The circuit of the motor armature 9 is now energized through the conductors 25, 29, 30, 31 and 32,- a resistance 33 bein included in series, and the furnace electro es are sepa rated by the motor to strike an are. When the arc is of predetermined length, the armature 14 leaves the upper contact, thereby arresting the hoist of the electrode 2.

Should the arc become too long the current becomes reduced sufficiently to cause the armature 14 to engage with the lower contact 35 thereby energizing the contactor magnet 36, current being supplied from the mains 22. 23 through the conductors 24, 15, 37 and 25. When the contaetor magnet 36 raises its armature the contacts 38, 39, are closed and the motor is energized to rotate in the reverse direction through the conductors 25, 37, 31, 30, 40 and 32, lowering the electrode \Vhen the motor is energized to lower the electrode two resistances 33, 41, are included in series as in this case gravity assists the motor. The field l) of the motor is constantly energized through the conductors 43, Both when raising and lowering the electrodes the motor 9 is broughtquickly to rest by dynamic braking, the resistance -14 being connected across the motor armature by the magnet 45, the closure of the contact 46 being assisted hr :1 spring l7. When the motor circuit is closed through the resistance 44. a mechanical interlock 48 prevents the closure of the magnets 26 and 36.

Should the electrodes he lowered too far for any reason, unduly shortening the arc and causing the voltage drop in the are to fall below the value for which the relay 19 is set,rthen the armature 18 will drop out and 0 en the circuit of the relay magnet 36 an prevent continued lowering of the electrodes. As soon as the. are lengthens by burning away of the electrode 2, or other causes, and the voltage .drop across the arc increases to the voltage for which the magnet 19 has been set, the contactor 18 again closes and the above described regulation is resumed.

charge will be :idjusted by the operation of the control mechanism, hilethe contacts 20 in the circuit 15 remain closed, the re lay 19 being set to open the circuit 15 at an arc voltage helow the usual operating range.

Should the supplv circuit voltage for any reason decrease unduly, the operating cur rent will fall correspondingly and the control' mechanism will cause the electrode 2 to be lowered correspondingly in accordance with the setting of the current responsive magnet 13. Finally the arc voltage may he redu'red to a point for which the magnet 19 has been set to open. This will prevent further lowering of the electrode 2. When the line voltage again increases and with it the line current, the control mechanism is free to raise the electrode 2, as the circuit of the conductor 16 to the raising magnet 26 has remained closed. The usual operation of the furnace, therefore, can be re sumed at once.

While I have explained and illustrated my invention with reference to the operation of a single phase are furnace, I wish it to be understood that it may be ap lied to the regulation of a furnace of a different number of phases, and that the character of the furnace may be otherwise varied without departing from the spirit of my invention.

hat I claim as new and desire to secure by Letters Patent of the United States,

1. regulating apparatus for an electric are furnace having cooperating electrodes, comprising a furnace circuit, means for feeding at least one of said electrodes toward the co-operating electrode to main tain an arc, and means for rendering said feeding means inoperative when the voltage between said electrodes falls below a predetermined value, while the supply voltage in said furnace as a said valtle;

2. A regulating apparatus fol-electric furnaces having lcctriid s i dapted to 'sup port an electric" ar'eomprisin a furnace supply circuit, an electric motor o"'el'atiifel'yconnected to at lemma ofs'aid'p ectrbdes, means for controlling motor readjust the position; of said elctrqdes in to variations of current in's'aidcnit and m'e z'in's made-energizing when-' an means when "we with Between SifiH' electrodes falls below} 'a' p'rdebbrininedvalue while the' voltageinsaid siipply'fii mains above said'valn'e.

3. A regulating'ap'para s for furnace having pairedifre atively an sienna movable electrodes comprising a supply circuit, mo-

tor means for moving 'at least on'of'said electrodes, means for controlling said in'o tor means in response to an electrical con,- dition in said'circiiit, and a circuit breaker arranged to dee'ncrgize said control means and having an operating coil connected in shunt to a single are between said-electrodes In witness whereof, I have heililltd set' my hand this 3rd day of February, 1920 JOHN A; SEEDE.

circuit is as great 

